erickson



J. ERICKSON. COMMON BAHERY T ELfPHoNggxcHANg rRuNKm 5x5 ,TEM-Y APPLICATION FILED MAR. 27, H3018. RENEWED APB. 9. 1917.

Patented Nm'. 12, 1918 fsHEETsfsHEU 1.

APPLICATIONFILED MAH. 27 '|908'V RENEWED APH. 951917.

Patented Nov. 12, 1918.

7 SHEETS-SHEET 2A A www ivm.. y ...u c

lil. I:

1.' ERrCKSUN. COMMCN BATTERY TELEPHONE XCHAN-GE TRUNKING SYSTEM.

l APPLlCATON FILED MAHfZT. 1908. RENEWED APR. 9 |917. 1,284,274.

Patented Nov. l2, 1918.

7 SHEETS-SHEET 3.

1,284 Patented N ov. 12, 1918.

' 7 SHEETS-.SHEET 4.

` Y 1. EmcKsoN. A COMMON BATTERY-TELEPHONE E-X-(IHANG` M E. S7. Y... S9 G., N9 mm N UA R Tw Ew Patented Noi. 1

1. ERICKSON@ COMMON B ATTERY TELEPHONIE EXCHANGE TRUNKING SYSEM'L muuu@ Ain mmh m8- MNM!) APR. 9. 1911.

PntedNov. 12,1918."

' l [SHEETS-#SHEET 7.

' .IOIIN ERICKSON,

OF CHICAGO, ILLINOIS, AssIGNon 'rO'AU'rOMATIC ELECTRIC COMPANY, or CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

COMMON-BATTERY TELEPHONE-EXCHANGE TRUNKING SYSTEM.

Specification of Letters Patent.

Patented Nov. 12, 1918.

Application filed Merch 27, 190B, smal No. 423,672. Renewed Aprn s, 1er/. serial No. 160,856.

y To-cill whom z'tmoy concern .i

Be' it'knowr that I, JOHN ERICKSON, a

' citizen of the United States of America, and

"residen-tof Chicago,=Cook county, Illinois,

have invented a certain newr and useful Imrovement in Common-Battery Telephone.

Xchange Trunking Systems, of which the following is a specification.

My invention relates to telephone systems in general, but more especially to automatic or semifautomatic telephone exchange systems, and particularly to systems in which the current for talking purposes is supplied to the subscribers stations from one or more batteries at the exchange or central station.

It Will y-be seen that` my invention ,is in i the nature of an improvement on the system disclosed in my prior application Serial No.

249,709, filed March 13, 1905, for improvement in automatic telephone systems.

prior application to common bat-t'ery 'workthat is to say; the combining of the essential features-of said `prior system with mea-ns for supplying4 v.talking current to the subscribers station is s own at A and the called' subscribers station. at A. These two sub- 'In the accom anying of a'telephone tion." Insaid ures the calling subscrib- `stations are shown connected through the medium ofA automatic switches and switch-- ing mechanism.- 'lfhe line of the substation A is provided Within double-wound individngi-relay' 42 and Aan individualbridgecut o n niln'iberllofkgroups. Allotted to each group coil '43. At C is shown a preliminary connector O r-nder switch, Sometimes called a preseleotor. 'It' Will be'understood that in the systemthesubscribers 'are divided into o fsubscribers'is'a certain number Of's'elecdrawings I `igures 1 and 2 -shew 'iagrammatically- Sa portion sgstem embodying my -inventors D, which are more or less a modified form of the switch disclosed -in United States Letters Patent No. 815,321, granted -March 13, 1906, to Keith, Erickson i and Erickson. i

at E, of the same genal type as D are pr0 Additional selectors, as shown vided, also in groups. The system also has connectorl switches F of the eneral type 'disclosed .in 'Letters Patent i o. S11-5,176,

granted March 13, 1906, to Keith, Erickson andEricksoh, but modified so as'to. adapt them to a common battery system.

Fig. 3 isa diagrammatic View illustratingI the construction and circuit arrangement of the 'finder operating device, which is/lan impulse transmitter, and which-is common to a group of subscribers.

Fig. 4 is a plan viewvof 'the said ini transmitter, and also shows several o the;

--line Or individual relays. The principal object of my invention is the adaptation of the system of my said` Fig. 5' isa top end elevation of the4 said' transmitter' shown in Fig.. 4.

Fig. 6 .is a section Online 6--6-of 4 l looking inthe direction indicated-bythe arrows.

Fig. 7 is a detail 'view showing the'posi- 'tion of some of the parts-shown in` Fig. 6

when the. Operating magnet is energiaed.

Fig; 8 is a detail 'section on line 8-8 in Fig. 5.

Fig.' 9 is a horizontalsection on line 6- -6 in Fig. 4, but looking in a direction opposite to that indicated by the arroWs.

Fig. 10 is a bottom end elevation of the' -said'transmitter shown in Fig. 4.

' Fig. 1.1 is a detallsection on line 11A-411 in Fig-9. w

Fig'. 12 is -a detail perspective of the interrupter shown in Fig. 9. f

Fig. 13 is a detail vieiv'oi. one of the controllingqelays 172, 190; etc., shown in Fig. 3.

Fig. Mais a diagrammatic view illustrating the construction and circuit arrangement and bank of one'or` the prim-ary connectors or finders.

'The substations may be oi. any suitable or approved type. ."Ihe'substation A, in connection with `which I 'have elected to Ico illustrate my invention, comprises a receiver 2, and a switch-hook 3 for controlling Athe substation circuits, which controllingo eral tions are accomplished through the me ium' of any suitable means. such as'ftho'cam arms 4, 5 and Cton the 'switeh-h'opk. IAs the -in telephones of this switch-hook is lowered the cam arm 5 mo- H wmentarily vpresses-fthe release springs` 4, 8v

and 9 into engagement. whereby the substation line conductors may be grounded sl- 5 mnltaneously. WhenthesuitrlPhookisdown l0 cuit is Anormally broken between the ground springs let and'l by the ramarm' G: b ut when said springs are together. ground. circuit is provi-fled t'o the ground post 17 and the release spring 7. as is usually the case I' type. The said substatioli also comprisesthe `usual transmitter. 18, and the induction coil 19 having the primary winding 20 and the secondary Winding 21. Being .an automatic substa- 20 tion it is provided with the usual verticalv and rotary. impulse springs 22 and 23.

an oblique projection or lug 24 on the under side, with which 25 teeth 2 5 are adapted to engagefoiw intermittently driving the spring 22 onto the ground .post 17. The rotary impulse spring 23 is provided with a similar mechanism 26 for driving the said rotary spring onto the" 30 ground post once'by means of the'rotary iin- The number-of 'impulses produced 'through f the medium .of the-'vertical impulse spring" '40 22 is accurately and definitely'determined at l each operation of the dialby the finger-"hole which the subscriber selects' onthe dial. It should be stated that a suitable 'stop is, Aas 1s Well known, provided tov always limitthe rotation ;of the dial., Whichstop' indicates'` when t'o release the dial. By referring to Fig.A 1 it will bev seen that theliinpulse'v springs 22 and 23: are' electrically connected with thefvertical'and rotary line conductors 30, and 31 that lead to the.'

' ,v not shown) j'which .i'sisecured to the-shaft- 1 a2; together with Aau. rocking dog 33# Furmaintains the fseparatioiiz of the ground spring-:$.14

tooth 2 7 are-carried onfthe 'periphery lo'f the fimpulsewheel' 36 whieh is secured to the shaft. .,'Ihesaid.impulse l-teetlrarefso arlposition the dog other.

Avertical impulse spring 22gis.pro\'i ded with lug the vertical impulse' example. on a.

v`supported in the 'bearing-53.-'f-ltisrialso 'provlde'd with a ratchet wheel "154 'ad-apted seen that the paWl isxlimitedfirrits'forward .thrust olf movement-by aiiadjiistablf stopthe impulse springs 22 and are not car ried into Contact` with the;grounthposi'. 1,7. said Contact oceurrlng onlv as the 'nnpulse wheel returns-to rest. In this operation the subscribefs vertical line conductor' Il() yis 70 first-'given a number of "ground impulses. and then the rotary line conductortll 'is given 'one grou'inl impulse. lt will be yseen that :1s-long as the'dial isoiit ot' normal 3B permits the 'I )rimary- 75 circuit.v springs 37 and to `separate. thus lpreventing the. impulses that-,are deliifered to either line conductor from .passing .to thev The means whereby the iuliscriber may-signalthe called sl'lbscribserjfcom 80 the push-lm ttonspring 39.1 u'hiehuior 'ally engagesthe contact lpoint 40; but when; the button all is pressed the spriugf); engages the contact, point 42, .whereby the-' vertical line eonductorO may,'beygrtulndedy The 85 line relay 42 (Fig. .1) may;consisty otany suitable doublefwoundvv coil equipped with switching, contact springs such as '442 .45 and 46. Likewise', tlie .bridge-'cutoti` relay 43 may be any suitable woundcoil-equipped 9.0 'with normally closed-v contact Vspringsvsuch as 47, 48'and 49. Said line and brid'golutconvenient or advantageous .position-as for I `relay Tackoi" suitable construction. I Y Y The .central. transmitting mechanism is set in operatonby the.lineswitching-'relay 42. Referring; particularly Atoi-Fig. .41. it` will be seen-that said mechanismconsists-oi a suitable frame or .body-5.0 adapte-d'to"']^ ro vide bearings-and supports forathesirarious operative parts and magnets. For example. the shaft l51 which .carries the"fwiper 52-2is to be operated :by the# pawl pivotally mounted on the -tarmatur'e 1 56 ofthegrftary magnet 57.- A-Referringto Fig. 9' it Sfwillfbe rt 59. of

screw 58 inserted through' thetp 'the said body. frame: i A Spring loeli-ing;may-

'attractegl-'izilhesi-tbe 1. thera'tchet wheel" rotated iiol' tions with the conductors leadingw to the .contacts of the vertical and rotary relays.

The said spring Wiper is preferably secured to'an insulated hub 66 (Fig. 4) on the shaft 51,' said hub being engaged by a brush or ,spring arm 67. With this arrangement. it will be seen that the conductor 68 (Fig. 3) lqoan be secured.v to the terminal of the brush 67, and 'that in this way the necessary current from ground to battery B is conveyed V(through the Wiper 52 Without including the shaft 51 in the circuit. The armature 5Gl also.carriesathejhisulated interrupterarm 69,; whichdtter is adapted to operatethc opening and closing of springs 70 and 71. This interrupter is .of the character diSv .closed in United Statesletters Patent No. 2D 831,875, granted .September 25, 1906, to A. E. Keith. The's id interrupter arm is providedat its end iith a lateral projection72 adapted, when the arm is attracted. first' engage the intermediate spring 73. 25. nd .tothen pass between the springand .the outer portion of the lspring 70` In so @loing it presses the outer end ofthe sp1-ing -71".,.0ut'of engagement withthe end of the 'spring 70, a piece of insulation separating 4the springs 73and 71. When the armature is released. the finger 72 again passes between the ends of the springs 73 .and 70', therebypreventing y,the springs 70 and 71 from reng'aging each other until after the armature has been. completely restored to its normal position. It will be understood. however', that any other suitable, known or approved arrangementcan be employed for producing an intermittent energizing of the 40 rotary magnet, 57. The cam 74 mounted 'upon the shaft 51v may be made ofvhard rubber or other suitable insulating material.-

5" "afterreleasing the said springs, makes a 64 before again engaging the said springs and returning the latter to their lnormal con-1 dition. Again Jreferring to Fig.. 4 it'will'- V "be Seen' that. the^ shaft 81 Vis 'supported on andpreferably arranged. par

beain 82 alle] wlth the shaft -51. 1 The springwlpers 83, 84 and' 85.111 'all mounted-pontile shaft' 81 and-'f Fig. 8)I ar'egfa and* from the heid sh'fjti-It i Iirnderstood,

complete rotatlonnin unison with'the wiper' own more chilly-in. l msu ated y fro?. each-futher of course, that these Wipers revolve in uni- -son with the -said shaft. The vertical bank contacts 'of the vertical wiper 85 are provided with terminals 8,6, the rotary banlc contacts of the rotary wiper 84 with terminals 87 and the private bank contacts of the private Wiper 83- with terminals 88.

These vertical, rotary and priva-te bank con- A' tacts are arrangedin the manner shown more clearly Ain Fig. 5 andare, of course, all insulated fromV each other. This bank is formed' on the are of a circle and is removable as a unit. C sequently the' said wipers 83, 84 and 85 a preferably double ended, so to speak, each Wiper being pro vided with opposite ends adapted to engage and. travel upon its allotted 'contacts In' vthis way veach Wiper is adapted to revolve' in a forward direction, and with one endrengage its allotted series or row of contacts immediatelyafter disengaging the. last. contact in s uch row or series with the opposite end. In other words, the. opposite ends,

of each Wiper arealternately brought into engagement with the contacts, the .arrangement being such, 'howeve1 'that while one end is in use the other end is'. not. The wiper 85 (Fig. 8) is insulated from the shaft and from the other wipers, but is in electrical 'contact with the metal hub or collar 89. In .this'way a brush or'spring contact 90, which bears upon-the said hub or collar, is employed for furnishing current to the said Wiper. The arrangement' ofthe other two wipers is practically the same, the wiper 84 being provided with a hub or collar 91 and a brush or spring` contact arm 92, and the private'wiper. is.

provided with ahub or collar engagedf by a brush or spring arm 94. As previously explained, these wipers 83, 84. alid-85` all rest upon contacts of the semi-circular bank. 95, and consequently the wipers, of; the switch are always in electrical connection.

witha trunk-line (either busyor nonjbusy) and' with the preliminary.connectpratthe .end ,of such. line'.- The 'motivegpropelling means for rotating, the

consists-of therotary magnet 96,. tlie'armature 97, the pawl 98 .andthe ratchet .wheel 99; The said armature is suit-.ably mounted and pivoted at 100, andthe said vpavvl is .pivotally'secured' at-101 to the upwardlyf,

projectingarm ofsaid armature. A spring 102 (Fig. 6) tiffany suitable character4 is' `er'nployed for keepingthe =paw1 ufixed lagainst l the`teeth of the .ratchet Wheel... .An adjustable stopsscrew. 103 limits vthee-'forward thrust or movement ofthe .said pawl, while I a' Spring -locking dog 104 engagesthe'- ratchetawh'el and therebyprevents 'backward rotation of the shaft upon which the vlatter is secured. A spring 1054(Fig. 6) is suitablyapplied to keep. the 'armaiuye 1 fao 97 normally away Afrom -thelQoite-opo1e" is" associated with each of these eighty-onel sets oi' contacts, such as the relay 42. Furthermore, it will be seen that the relays 167 and 171, and those between these two relays, constitute what Amay be called the vertical relays-of the switcli-operatin machine, inasmuch as they control the di erent l circuits over which the vertical impulses are transmitted' by the said machine foroperating the vertical magnets ot' the preliminary connectors. On the other hand, the relays 172 and 173, and all of the relays between these two particular double-wound relays, constitute what may becalled the rotary relays of the switch-operating machine, inasmuch as these particular relays control the different circuits` over which the said machine transmits the rotary impulses for operating the rotary magnets of the prelimi- `fnai'y connectors. Consequently, the nine relays to the right of the line X-Y control -,the tens digits of tlie numbers of the subscz'ibersin this lparticular group, while all ofthe relays to the left of said line control the units digits of the said numbersthat is to say, determine the impulses for such digits. For example, ifsubscriber #22,11 takes down his receiver, the result of such ac t would be the energizing of relays 172 and IS7-that is to say, of the inner coils of these two relays.

the relay 172 to send first only one impulse on the vertical side and then one on the rotary side,'and by relay 167 to send in only one' impulse on the vertical side again and one on the rotary side, thereby in effect call;

ing his own station'. Again, should sub-` scriber #2299 remove his receiver from the switch-hook, the result would be the ener;

gizi'ng of relays'173 and 171, and. in this' case the switch-operating machine will first transmit nine impulses onthe vertical side and one o n the rotary side to the idle or waiting preliminary connector, and then nine on the vvertical again and one on the rotary. With this arrangement the first tensl relay 167 coperaties with the first units j relay, or with some other velay' at. the left of line X-Y, according to the number of the culling subscriber to find the line of the calling subscriber when the tens digit of that subscriber is one; and in .like mannei' the second tens relay 168 cooperates with someone other relay at the left of the line X--Y, according to the number of the c alling subscriber, to find a calling subscriber whose tens digit is two, etc. Invariably then if the tens digit of the calling subscribers number is five, for example, the. taking down of the receiver at this subscribers station will result in the energizing of the inner coil of the fifth tens relay 178; but if in any case the tens di rit of the callinv subsciibers number is eigit, for examp e, then the uIn such case the switch-operating machine will be allowed by eighth tens relay will be energized. On the l other liand', and invariably if the units digit of the callin subscribers number is five, the result will be the energizing of the lifth units relay; but if the units digit is eight, for example, then the eighth units relay will be energized. In any case, however, it will be seen that the energizingl of a certain tens relay, for example, makes it possible for only a certain number. of the tens contacts to receive andtransmit impulses from the. wiper 52 to the-'vertical magnet ofca preliminaryv connector. maining operative corresponds to the number ofthe energized tens relay, and all of the tens contacts above .such lnumber are' rendered inoperative to transmit impulses when engaged by said Wiper. This is also true, of course, with respectto, saidv units, relays, inasmuch 'as the energizing of- 'a particular units relay cuts out, so to'speak.

all of the units contacts above the number of such units relay=-that'is, if the'thrd units relay is energized only the first three rotary.

contacts Will lremain operative, while the other seven will be rendered inoperativeby The number of'contacts thus rej reason of the ap or break produced in4 the circuits, It will be seen that the linerelay contacts allotted to and.emp1oy ed for clos'- ing a ground connection through any particular tens relay are all multipled together by means of one of the horizontal conductors shown in Fig. 3.' In a similar manner the line relay contacts which are allotted-'to and employed vfor Losing a' ground. circuit through any particular units relay. are all multiplcd together byvmeans of one of the conductors shown extending at right angles i to the saidl horizontal conductors.

When a subscriber starts to call another subscriber, the act of removing the receiver operates his line relay, which inturnfstalts the transmitting apparatus. This apparatus must, of course, complet@ i125 "Operation before' the operation of call 11g the number 0f `11,: the desired slililsctglberis. egim, and ncenfgf'. in the interval l"b `et'weei i the removal of the cally calls the station of the calling subscriber. In other words, this apparatus au toinatically transmits impulses correspondscribers number, causing the preliminary .lng to the last two digits of the calling subconnector or finder (l (Fig. 1) 'to select the' bank contacts of. the calling silbscrbeifsline. ln this way the culling subscriber, by

' [to begin l(falling the deslred number. Bv,

I simply ,removing .the receiver, or .in any if other 'suitable manner, automatically calls his o\\'n-liue,' vso to speak, aud thereby establishes connection with an idle trunkline running 5. tolza--so-ca'lled first-selector, or to sonic other l519..,31tch.- LAS soon' as'tliis has been done the subscriber isthen ready to-lwgm-the operationotcalling the desired number. Bnthe 'isonlyeonnectedfwlth the saulrsty' ifectorg' l, 10oraptherswitch, from the time-the i 'eliiiiinali'e'onnector seizes ther calling'`l ine"iiutil` f theswitches are restored to their normalfpof Sitionsr- Thus there [are no individual Vswitches, the line relays bei-'ng practically -v 115V 'the .only devices` whielrare 'made individual `to fe'ach other. Obviously, therefore, the .number of .so-called tirstselcctors, and other necessary switches, may be considerably less' in .numberrthan the total-number of sub- 20sci1ibers, with the `result that'the'apparatus .is simplified and materially reduced without Vin "any-way reducing the e-tlioi'encv of serv- I ice. between subscribers.- This'is, of course, 'largely (inepto-the fact that the central 2i;v transmit-ter switch (Fig.v after connect:

' ing the calling subscribers luie, with one ot -tlie first=selectors returns'to its normal con- 'dition :and -rei'iains '1n readiness for use bylanother;subscriberof the saine group. 'i lVith' '30 this arreaigenlent.,Y..therefore,l the Aswitch show-nein Fig. -3 is.alwaysin readmess to be.

' employed'lyimy Subscriber vof the' group jor the-purpose offconne'eting his linefwith :an idle"rst-selector. Thus,.not-withstandvselective switches which are individua-l .to tlie'subscrilgers. vthe operation, as far as the "cally I the vsame as if each lineteiiiinated gs'erber.'Uv livsimply f relno'vingv his receiver fio'i'n" the" usual f' switch-hook, 'a utomatically -fstartsa tra-iu 'of elect rieal steps orjoperations 'h'icl'rfare completed bythe time-he is' ready .this`in-ai'is', without an)r hesitatitiiioryaddift aljwor on-the part'. Vof t'liecalling sub- )scribe hegotf the called number@ I "ronithis on the apparatus and the'. operation ofan suitable." mown or approved er. mv invention relating;r more parf ltit ulal. v t oiluitq'rart of the operation wliicli isingrlii'ded between' the time vof the 'taking doivtuof',the...receiver of4 the callingr subseriber',an,l .the conse nent,.ailtpmatie-conon unithzgan idle. rst-selector or other `The"derices" used from then on er pondi'ng' to (meormore digits. as .the case illing'the desired number. endfor com vpleting -theeonnect-ion through to the" called 'subscrli "s line,.may be of any suitable, know rapprovcd character.

, Kill assuniethnt-the subscriber at sta- AjztFigj 1)', whose number is 2251,v deetres to' converse with the subscriber 'at stavthereby produce a momentary engagement o f the switeh-hook projection 28 with the switch conta-et 20. This, it will be seen.'mo nicntarily grounds the subscribers liney conductor 30.A the circuit thus momentarily formed extending l:from ground 'G' through. the c'ol-ieratine ground springs 14 al'idl'to the contact point 29, thence to the' Contact point Q8.s\vitchhook 3, over conductor 174, vertical line conductor 3Q to the rel1y42 springs 48 andai? and to battery lead 219,

,.t-henc'e through battery B to ground G.' ln

this way the removal ot the. receiver momentarily rounds one 'side ot' the pulling subscriber-S line. 4with 4the result that the lre la)v 42. which is normally bridged across the subscribers line, is energized suliicie'iitly to-I attract the armature' 176. `This relay 42 is 100 normally connected by the. contact springs 47, 4S aud-t9 with the nou-grounded pole ot' the battery In other words. Ythe momentary grouudingof the subscribe1"s line coin- 'p'lctes a temporary` circuit includil'1, 1f the coil 105 @and the battery B. 'When thus energized the subscribens line relay 42, by attracting the armature 176., causes the normally sepa`- "rated contactsjfit, ouml-4 6 to be bremight;'A

energizing of relay 180 which also attriicts tsva-rm'ature, Simultaneously with the for-` mation of these lcircuits-and the emrgizingftl of these relays, however, nnothe'r eircuitis 1 closed `from ground through Contact airn to conductor 132, thence over inner relay coil'17:2,.overconduetor .179, through coutee-t spris mrd through ,reay eoi 18,0 and over the conductor 18'1. to battery B 130 and thence to ground G. Obviously, with the arrangement shown, the inner relay coil 172, when energized, will cause the armature' 183 to break Contact with the contact peint 6 184.v Likewise, the inner relay coil 178 whenenergized as described, attracts its'armature 185, thereby causing` the latter to break contact with. the Contact point 186.

. At the same-time the energizing of the relay 1,0 coil 180 will cause its armature to engage the contact point 187, thus closing a' circuit as follows: from battery B through conductor 181, Contact 187, armature 188, rotary magnet coil. 57, thence through the normally en gaging circuit-breaking contact springs 70 and4 71 to ground and back to battery. This rotaryvmagnet, when energized, attracts its armature 56, causing the latter to separate the contact springs 70 and 71 and thereby permitting the armature to be instantly released. As the armature 56 is alternately attracted and released, owing to the make-andbreak action which it produces in the-coil 57 the spring wiper 5 2 is given a step-bymotion over the saidcontact teeth or Step switch contacts. lThe spring wiper 52, as shown in Fig.v 3, is part of an electrical circuit, and as it makes the first rotary step the anode 75, which is attached to the same so shaft, breaks Contact with the spring 76, thereby allowing the latter to in turn break contact with the spring 78 and close Contact with the spring 77, at the same time allowing the contact spring 7 9 to make contact $5 with the spring or switch contact 80. The contact springs or arms 77 and 76, when brought together, serve to establish a. cir- -cuit from round through the relay winding 189 (whic is on the same spool or magnet as the coil 172), through the corresponding winding 190 on the next spool or magnet, and -thence Athrough all the corresponding coils of the other sixteenmagnets shown 'in Fig." throlugh conductor 191, contact ,a springs 77 and 70, coil 180, condi tor 181 paratively slight, sothat the armatures 183- and 185 which, `it will be remembered, are already in contact with their respective polepieces or magnet cores will be retained in contact therewith, but none of the armatures of the other relay magnets will be attracted. The armature 188 of the relay 180 will, however, 'be retained in contact with itspole- 60 'piece or magnet core, thus maintaining the continuity of the previously closed circuit through the rotary magnet 57 and its circuit breaking contact springs and 71. In this way the said rotary magnet'will continue 65 to rotate its" sha-ft,l and thereby keep the `ten automatic preliminary connectors shown' to battery B, and thence to ground Prefspring wiper 52 moving until the latter. has made a complete revolution. Itwill be seen, ofcourse, that the cam. 7 5 will also make a @replete revelsten- 'siaseltaeeously wththe said wiper and will, as it returns to its start- 70 1ng point, agai n m'ake Contact with contact spring 76, thus pressing the-flatter out of engageme'nt with the contact spring 77 and agaln closinp` Contact with thel arm or spring 78. Thus is broken the circuit just described 7'5 from ground through the windings 189 and 'A 190, etc., in series through the other series. A relay windings, through conductor 191%, coni tacts 77 and 7 6, relay-coil 180, conductor 181, and through battery B to ground G. In- '80 stantly upon the breaking of the 'circuit the relay coil 180 will allow its armature toA re. turn to normal position, thus breaking contact between said armature 188 Uand the con'- tact 187, and thereby` opening -the circuit through the rotary magnet 57. At the' same time the said armature 183 of the relay coil 189 will .return to its normal'position mengagement with the contact point '184,' and armature 185 of said relay 178-will return to 90 its normal position in engagement with the contact point 186. Obviously, however, and during'the time that the spring wiper 52 is making vits revolution romfstarting point on Vthe contact 191, certain other operatrons will take place, with respect to whichA the 'following preliminary explantion is made The wipers or switch arms 83, 84 and 85 shown in Fig.'8 are diag rra'mmaticv representations of the spring wipers shown in Figs. 4.and 5. It will be seen that the ten sets of oontact teeth, such asthe set 203, 204 and 205, the set 205, 207 and 208, the'set 209, 210 and 211, etc.,.are each connected with one of thel at the left in Fig. 14, and nrevously referred to. For convenience of illust;` tion 4only one set 'of these dlerent connect ons is shown. The echt-aat peint aos. is shown connected with Vthe conductor 212: c ontact point 204 with conductor 213; vand contact point 205 with conductor 214. These three conductors lead to the so-called. preliminary connector or other suitable automatic switch shojwn in Fig. 14. As shown, the arrangement of cirl cuits is such that the spring wiperszSB, 84 and 85 will never rest (exceptl for a v,brief instant) on a set of contacts connected with a preliminary connector which is busy or already in use. which prevent these wipers from stopping. on a set of'busy contacts are as follows:

.,Suppose. for example, that thesewip'ers 83,-

84 and 85 should for any reason whatever be moved about and so adjusted 4that the 1 25 -wiper V83 would engage the contact point 203, wiper 84 engage with .contact 204, and wiper 85 engage with contact 205, it being understood that these three contacts constitute one of the ten sets of cont-acts involved The circuitsg, and means 120 iii the construction of the bank of 'swit'eh 'oiitactb' Shown in Fig. 5. :unl :i lso assume, foithy purpose of this illiiStratioii. that the pretablisliinga guardingfpotcntial at the eo'ntact point. Q03, by rason of fits temporary connection-ivitlr-'th'ev grounded pole of thel battery.

15; the;contact-pont203, a circuit. will-be closed froni- ,aground G? A`through `conductor 212.

throughcontare-t point 203, springwiper '83.' Y

eondiieior218, contact.-sprin'gs` 108 and 10T.

iuiil through ,tli'cfeil -96 to battery B, und.

20 thence gt grouinl G. This will vGiiiisietlie r0- tary magnet coi-MN5 to attract' its-armature, and by means 'alreadydescribed.inflnee the slia't'tto-.w'vhieh .the spring wipers'. 84 and H5 are :jlttachilut'o instantly make'one rotary- 25 slop., iherbycarryingthea@"wipers oiitof',

also momentarily be e'oiiiiel'ted to grou'n'tl'as A' position.'rv lll'owerei.r in order that`a-` botter under-Standing ofjilie :ei'rcllits may' he li'ail.

rr co'n-iieetor l( Fig. 1 `eoiiiieeterl with` L{()hiioiisly,V as the Spring wiperI .G2-is given and lrvnieaus' of the pawl and ratchet'derice alread)Y described the spring wipers 835 S and will he movedl forward-ono step anfl onto Contact points 20G, 207- aiid '208, so as.t0 'be-ready for the next 'call-*sentiva 70 from the switch-operatiiig maehine. y"1-`hese" 'wipers will, however. rcinaliron contacts 203. 5204` andv 205 during the v'tiinatliat the spring wlpelg '52 4is making its' revolution.V

ay step-by-step in'otionover itsicon'taet .points 191, 192, 193,' 194, 19.7,' etc.; throughout.` the Sets of eontacts in the, liankand just att-licf' timwhen 'it rests onA each new eontaetipoijnt,1VA it is connected vto ground through the. v'eoii'' duetoi' 6,8., 1'e0ntaet spring 70,:iiiil` 'contact-,- spring;r 71.v 'Thisa'it will be. Seen. yis for thai reason that' ii'heiie've'r the wiper-f2 -lests on* a contaet point'4 thne'arinntiire 56 v-ali'irw from 'the eore, 4or polemieee, of it-s' iiignet 'angl eaeh time thatthe armature, .'iis drawn iip 'against its corel or polo-piero. contact is'.V` thereby broken betwee'ntlie springs-170 and 71'. 'the resultheing'tliatthe veontaei iirn't'n't 7 wipl-r?. as it is 'stepped oreiits teeth, will it rests on :each toothin its path"oftrareh" The etl'et oftliis action will he readi| i'i ii (ler-stood. -forns the eoi'itact i'riuorfwiper 52 rests on the, eontaet' pontfl92 a eil-Cuit; 95

f lie ist,v

v' contact-.point .through the contact point 196, condudtqlf.. `0, f co1 1tact5.pomt-231, v

gpoint-.2281armature229, 'contacty point 226, armature .227, jcontact'tpoint '221, armature lpoint 186,.f-'so htthe spring wiper 5 2 will :then-belinea 'able o .f'eiecting the transmis -"'.sion^.of 'lfnrt er vertical impulses, and will cuuSetheztransmission oilnoimpulse or im-A lpulsesof-.a'ny kind whatever until it passes v4from-:the contact-point201 onto the contact f -tary` li neto theitotniy magnet-112v of the preliminary connector switch. C. It will .now. be .seen that. ve impulses, correspondber'. ofthe callin subscriber.. ,have been transmitted throng the vertical magnet-111v of.l the, preliminary/ connector 'switch' C, thus f' raising-the wipersfof this preliminary conthe, cinte-.ofthese wipers. will be opposite the fthnrow. ofco'ntact teeth, -and thus molde of ythe sw-itchoperating, machine, Contact'. 1point;ollendiictor1213,.;'otari magnet 112,A

vL eifcoin-lucto'11219, through battery Bto ground thus. causing 'a single rotary impulse to "be sentv through "the rotaryfmagnet This'causesthc switch slm-ft of thepreliminary; connector to make one rotar)r step, il'ncingtlic shaft wipers 281' and 235 in contat-t with the switch, points 237 end238 'of the liu-nk (j (in'tactsV allotted to this switch, alulalso causing-the private wiper 236 to =be placed in 'electrical Contact with the con-` all Vtactpoint2 39fifn' u .so-called private bank o l 0 196, were it, again leffectsthe transmissinvro Ian. electrical irnpuI se armature' l232, contact l two digi-ts ofthe numb will ynot and cannot eiecty;

of .another vertical. impulse isdi-lefy to the .fact that armature 185. f'ofithe-.icoil- 1-.78 isgat suchjtime' drawn up," :thereby- :breakngf contact. with the contact mence to-send rotaryimplllses over the ro-v tion has been terminated. Whentlie bridgeing.. to the digit inthe tens place of. the num- '-ner previously' described -turns to origin al position, .thus

the preliminary connector switch Chas completed its operation, having placed `the line' wipers -234 and235 on the @tiret set of. con- `"mets of tiie'itl row er level in ,the bankof line contee-tait beingobserved .thatfthis bank 1s made .up of pairs. of' contacts, each pair consisting of twofoontncts connecting/with the opposite vsides of a subscrberlslinef In other words, connection is made' with the sot of 'contacts which corresponds tov thelast verof thecalling subscriber, thus-'completing the connectionl thelnies coming in from telephoy 5;#2251 through the conductorshQftO. andpll, line wipers 234 and 23.5 to the trnnkline conduc- -tors-fleadin t0 a' regular .first-selectors. as

shown in ig. 1,.or -to 'anylother-sttable at' thi'stim'e a`circuit is also"es tab1ished through-the br'dg'ercut-oif relay 43, this cuitxbeing :from ground throughthe. rvate wiper 236, contact'pont 239,' throng rely coil 43, thence through-battery 7B to ground G, thus causing thecore of the coil 43 to attract the armature 242-, .erifectingthe retention of thisfarmatre in .lits attracted position until the preliminary.` connector switch C is eventually releasedand 'restored to its normal' condition after the conversacut-off relay '213 attractsv 'its 'armature'it breaks contact between the switch sprin or contacts 47, 48 and 4 9, thus opening4 t e bridge normally'closed aci-'ossi the lineoonductors 3Q and 31 lead-ingr from telephone #2251, This bridge includes. the line relay coils of the-'windings 242 and :243'connected normally to batter-y throughgthefsaid' contact arms. ing subscriber free frombridges of .this character and putsjit ina'condition frvsubscriber #2251 to operate there' ular; first# selector, second-'selector-,thrd-se coton. etc.,

.and -the regular and] usual bpcorulectorj lt -110,

will -be seen lthat the. wipes-'52, sitter leaving the contactpoint 201,"passes n hernanthe contact: same time 'the cam-I 74 'a Spring Rwaiy and into' engagementw liltlie'contact spring 78, and als'obreaking.. .contact between the contactfspring 79'a`nd 80. 0bviously,.with L20 the arrangement showmt'he Contact` spring 76, as it breaks. away fromthe-springzf,

- 'serves to open the previouslvidescribed' clrcuit from ground to the coi1si189 and 190, and all of the coils in series-,Zas shown in 1 26 Fig. 3. This action. having been accompl1shed, they armature 183 returns .to its original position 'in engagement with Athe contact point 184` .Whilelthe -arrnature185 of t e coil 178 returns to its original posl- 1an This leaves theliner-fjthecalL' 1305 f y 1,284,274 f f tion in engagement with the contact point raised'to the second bank level and brought 186. It will be seen, however, that this ciropposlte lthe first contact of said level. The

uit also .includes the relay coil 1 80, and energizing circuit for the said vertical mag- .the latter consequently releases its net 115 extends' from ground G through .alrmatuta` thereby breaking contact between the springs 129 and 130, private springs 124 .70

' lthe Contact arm 188 and contact point 187, and 123 to the vertical magnet'll, thence to and in this way openingr the circuit from the battery lead 219, and through battery B ground through the rotarymagnet coil 57. to ground G'. The rotary impulse spring This, of course, .results in bringing the 23 is thenpressed onto the ground 'post 17, nl wiper 52 to rest on the contact point 191 grounding the rotary line'conductor 31 and 75 where it remains until a new call is sentenergizing, therefore, the rotaryllnev relay lin from any other .telephone of this particuf 127 of the selector D. The energizing cur- 4lar/group of subscribers. It must lbe borne rent passes from ground G tothe rotary in mind, however, that another circuitis line conductor 31,- conductor 241, contact ,15 opened through the rotary magnet 96, owing point 238,'1ine wiper 235, line conductor 8 0 to the separating of contacts 79 and 80, and 245,'side switch wiper 120 of the selector D, y consequently the magnet 96 releases its armacontact point 247 to the rotary line relay tura-whereupon thepawl of: the armature 4127, thence to the battery lead 219, and V97. 4engages the shaft 1 carrying the `spring through battery B to. ground G. The ro- 420 wipers. 83,84. and 85 and thus moves the tary linerelay. 127, upon energizing, presses S5 latter into engagement with the contact the line relay'spring 128 onto the ground points 206, 207 and 208, where said wipers spring 129, thereby establishing a circuit are ready to receive the next call coming vin through the private magnet 118 from from the calling wiper 52 in-response to ground G'through the springs' 129 and 128v 25 the removal of a telephone receiver from its to the private magnet 118, and through the 90 'hook by some other subscriber. said. magnet toA battery lead 219, thence .l y The methodof calling the desired number through battery B to ground G. "The priis as follows: Assume, or example, that the vate magnet, upon energizing anddenergiz-- SubSCI'beI at Substation'A desires to call subing,.permits the selector sideswitch to pass 30 -scriber at substation A vto which 'is allotted from first .to second position, allowing the 95 the line v2299. .To 'call the number 2299 the side switch wipers 121 and 122 to engage the subscriber at substation raises his switchcontact points 253 and 254, respectively. h ook andthcrebv automatlcally obtams a The closure of connection between the side Y trunk-line which 1s not'busy, in this case switch 'wiper 121 and contact point 253 sets gtll'mklr vollduotqrs1244 and 245 leading up an energizing circuitJ for the rotary mag- 00 to a rs't-4 Selector DQ When the dial is net 116 from ground'Gr8 to the contact point .drawn down for the 'first digit, then -upon 253,'through the side switch wiper 121, interreturning tonormal position it operates the rupter spring 125', rotary magnet 116 to the lfirst-slelector switch't'o 4establish connection battery lead 219, thence'through battery B '49, with 'an vidle trunkdine leading toa scondto groundG. The said rotary magnet then 105 ,selector In" a similarmanner, the seooperates to rotate-the wipers 248, 249 and 'ond-selector E is operated for -thesecond 250 ofthe selector D intol engagement. with digitfto select an idle trunk leading to a conthe first contact of the second level of the if' 2 .'nector"switch F. The impulses* for the last selector D, from which Contact it is assumed two digits are directed towardthe connector that. the trunk-'line conductors 255, 256 and. 110

' vF,"'which operates to place its shaft wipers 257 -lead to the second-selector If the in connection with the contacts correspondfirst trunk is busy, however, and the 'wipers ing to the desired line. The rst digit behave to pass over busy trunk-lines, then as ing 2,- the spring- 22 is pressed against the 'soon as the private wiper 250 engages the j ,"50 "grondp'ost 17 twice. As aresult, the verr'st grounded privatev bank contact point, 11.3

' f' .tical-liner rely -126 0f the first-selector D the private magnet 118 again energizes, lockv Xi s' 'jenergized each time by a owof current ing the side switch in second position., l from the substation ground 1 G, through energizing circuit for said'private 'niagrret 'springs -14 and 15 to the ground post 17, extends from the grounded terminal G of 5 thence through the spring 22 to the vertical battery B through an occupy-ing switch (not 120 'p line A conductor]l 30, conductor 240, Contact shown) tothe private wiper-250, thence over I, 'Y `point 237 ,line wiper 234, trunk conductor the conductor 259' and through the back-re- 5244,-v side' switch Wiper-'119, contact point lease relay 133 to the side switch wiper 122,

'i 246, vertical line relay 126 'to battery lead contact point 254, private magnet 118, thence 60s-219,- thence'through battery B to groundG. through said magnet to the battery lead 219, 125 Eachtime that'th'e 4vertical line relay 126 and through-battery B to ground .G. When energizes, the line relay spring'130'is pressed thusenergized'the private magnet 118 locks' I -onto the ground spring 129.A vThe vertical 'the side' switch in second| position `and the"` magnet 11,5 is thereby energized, and the wiper 121 vin engagement with the contact wipers 248, 249 and 250 of the selector D are point 253, thereby the rotary: magnet 116 -160 will be energized step by step until the wipers are carried .beyond the last busy trunk-line. At the instant that the private wiper leaves the last busy contact point, the

venergizing circuit through the privatevmag- 'net llisjdestroyed, and as a result the selector side switch passes to ythird position. If, however, there arev no busy trunkdines, the rotary magnet 116 releases the side switch to third position as soon as the wipers are carried.- into engagement with the first trunk-'line As soon as the .side switch passes to. third position, as stated, the subinterference 'subscribers line thus extended, but a' guarding-potential is establishedjat the private wiper 250, lwhen the Side switch wiper ,122 assesV onto the. 'ounded contact point 262",

' or 'prote'ctin't e'seizedtrunksline against y other calling 'subscribersff This guarding"A potential is established'-from "ground G to.` the eo'ntactgpoint 262", thence rough'the side Switch'wiper 122, through the backrel'easefrelav 133,l conductor 259to the privatewiper250. It will be seen, of course,- thatthe venergizin circuit for the rotary 'magnet 116 (to'whl'ch reference has already beemade) is :destroyed when the idle trunk- 'line-isf seized-#that 11s, when the side switch 'wiper 121`lea`ves' the contact point 253. The '.seconddigit' `of the-called member being 2,

t the 'calling'subscriber again operates his dial accordingly; as a result grounding the ver 'tical-line'v conductor 3 0 when-the spring 22 meets" the ground post 17 The vertical Vline relay v141 "ofthe switch' E is, therefore, energized twice by a flow of curr'ent from the substation ground G to the vertical line condufctorg 30, `thence through conductor .240,

. 'contact point 237, wiper 234, conductor 244,

side switch wiper 119, contact point 263, condu'ctor 264, switch wiper 248, contact point 260,' conductor 255 to the vertical line relay 141,'th`ence .tothe battery lead 219, and

. through battery B to .ground G-that is,

whenl the vertical line conductor 30 is groundedjfor `thoseicond digit, an energizmg circuit is establishedthrough the vertica magnet 134 which 'operatesto carry the shaft wipers 4265, 266 and 267 's'tep byl step to a position opposite the bank terminals of the second level', Whenthe rotary line conductor'l is grounded after the vertical impulses, the rotary line relay 140 is energized, whereby an energizing circuit is estabished through the private magnet 137,

which in turn operates to release the side s'witch,-as .described lin connecton'with the selector D. When the switch E comes to rest, it is assumed that the sha-ft wipers 265 and 266 'stop in engagement with the conductors 268 and 269, respectivelyas shown, whereby tne calliing subscribers: conductors 30 and -31 are-extended tothe connector switch F. Thev ground impulses from the substation `to the lineconductors or the last two digits, namely the third and fourth, are effective in operating'tlie connector F. The third digit is`cal1edafter the subscriber has established connection with the connector lF by wa "of Ithe trunk conductors 268 and 269'. The subscriber rotates the dial as'described for the thirddigit 9, thereby grounding the verticalandv rotary line conductors 30 and 31, 'whichfin 'turn causes the energiaation of the connector -vertical androtary line=relays 152 and v153", and also of the d ierential relay 165. .The energizing'current flowsover the following path From groundgG' to 'the' vertical f line conductor 30, trunk onduetorsamora, 264, 255 and 268, through the'windingfofthe'vertical line relay 152- and winding 270 ofthe-' differential coil 16,5V to tliebattery'l lead12219, thenceA through battery B to ground ,"G. Eachftime that the vertical magnetf156 is energized it vraises'thesha'ft and wipers'153, 154 and 15.5 one step at a time until .the'said wipers are carried nine steps end brought opposite the level in which are vlocated the terminals of the line 2299. When the rotary line conductor 31 is `grounded the rotary line relay '153a and thedifferential-rela'y'165 be come 'energized' over the followingpath:

From ground. G. 'to the rotary line conductor 31, trunk conductors 241, 245, 271,

256 and 269, throughV the windin 'of the rotary line relay 153 and win' ing. 272 of the differential relay 165 to .the back-- vbridge relay springsv273 and-274 (which are normally -in Contact) 4to L'the batteryl lead 21.9, thence through battery B to ground G.-"The energization of the rotary line relay 153* vcauses the springs 277 and 278. to come'into contact, thereby completing a circuit 'from ground G9 through the private magnet 4159 to the backibridge relay spring's27 3 and 274, thenceto the battery lead 219, and through battery B to ground G. The momentary energization of the private magnet 159 causes the lrelease of the side switch from first to. secondjposition, thus placing the sideswitch 'wipers 162 and 163 in contact with the points 279 and 280, respectively. .The last digit being 9, the subscriber operates the dial as previously described, grounding the vertical A"line con.- ductor 30 nine times and the rotary line conductor 31 once. The vertical and-rotary line relays 152 and 153a are `.ope1 1tei 1 over the previously tracedv circuits. However, When the line relay sprin s 278 andA ,281 engage, a circuit is then c osed through rotary magnet 157 instead of -throu 'h the the vertical magnet 156. The circuit may be I' traced from ground G to the line relay `springs 278 and 28,1, through the springs 294 and 295,: side switch wiper 162, contact point 279, through the rotary magnet 157 to ithe battery lead 219, thencethrough battery B to ground G, Each time that the f rotary magnet is energized the rotary armanumber is 2299.

ture is attracted and rotates the shaft carrying the Wipers 153, 154 and'155 one step at a time, until the said wipers are carried into engagement with the normal conductors 282, 283 and 284,"the first two of which lead to the line. of the .`desired subscriber, whose The energization of the rotary line relay 153a for the last digit 'cour pletes an energizing' circuit through -the 'private magnet 159, which now operates tion, or the so-called busy-release of the conwith one of two results, namely the release; ofthe side switch from second to third vposilnecto'r. if the called line is busy. Suppose the former result to occur and the side switch to pass to third position, thus placing' the side switch wip'ers'160, 161,-162 and 163 in contact'with the points 285, 286, 287 and 288, resyiectively.l When the sideswitch wiper 162 engages the contact point 287 the ringer rela 158 comes under the controlof the vertica line relay 152 in the same Inanner in which the rotary magnet 157 came under the control of the vertlcal line relay when the side switch passed from first to second position. Furthermore, when the side switch passes to third position a guarding potential' is. established for the protection of the called. line. This guarding potential extends froni ound G1 to the sideswitch wiper-163, t ence to `the shaft wiper 155 which now engages the privatecontact of the .called line. tial at the private wiper 155, furthermore, causes a How of current to be sent through the bridge-cutoif relay 289 from the said private wiper 155 to the private normal con# ductor v284, to the bridge-cut-oi relay 289,

thence to battery lead 219, and through battery B to ground Gp The said relay, upon energizing, operates to separate the springs 290,291, and 292, which are normally closed,

thus removing the battery current from the individual line relay 293 and rendering it inoperative byy any impulsesfrom 'the sta- To signal the called subscriber the calling subscriber presses the signaling button 41, placing the spring 39 in Contact with the substation ground Gr', 'and thereby energizing the Vertical line relay 152 -from ground G .through the springs 14 and 15, Contact point 42, 'spring 39, springs` 37 and38 to the vertical vline conductor 30, thence over a path previously traced. When the vertical line relay 152 becomes energized the dierentiai reay 165' is also energizedthrough the winding' The said guarding pot en.

naamw.v

27 0. The armature is attracted and the 'springs 275 and 2764 are lplacedjn contact, thereby completing the energizing 4circuit extending from ground G9 through the springs 277 and 281, private magnet springs 294 .and 295, side switch wiper 162, contact point 287, through the ringer relay 15,8, differential relay springs 276 and 275 to the battery lead 219, thence through battery Bto ground,G. As a result the ringer relay becomes .energized and its armature causes the springs 296 and 297 to make contact with the rlnger generator springs 298 and 299, respectively. As

avresult ringing current ispermitted to 'pass out on the line of thecalled subscriber, which current passes through the substation ringer 300 lands'ignals the subscriber. This si aling current passes from the generator to the springs 299 and 297, sideswitchfwiper 160, contact point 285, shaft wiper 153, normal conductor 282, vertical line conductor 301, condenser 302, ringer 300,V springsl 304 and 305 to the rotary line conductor 3'06,`nor

.mal conductor 283, shaft wiper 154, -contact point 286,*side switch wiper 161, ringer relay springs 296 and 298 and bac-k to the generator R. As soon as the calling subscriber releases his signaling button 41 the currentthrough the vertical line relay. 152 and-differential relay 165 is interrupted, denergizing the said relays, whereby the ringer relay returns to no rmal position.v As the called subscriber removes his receiyerf'308 from the switch-hook 309 the latter, upon rising, de-

stroys the ringing circuit through the'bells 300 at. the instant the springs 304 and 305 separate.` The switch-hook, on rising, also closes the primary circuit springs 310 and 311, thus closing a circuitthrough its own station that provides the transmitter 312 and cil 314 with current for talking purposes. The current for this" circuit passes -from ground- G1 at the connector to -theY side switch wiper 163, tofthe winding 315 of the relay 166, ringer relay springs 307 and 296 to the side switchwiper 161,' rotary.line

wiper 154,1-1ductors 283 and 306, primary 'Winding 313 of the induction coil 314, transmitter 312, springs 311 vand 310 to the .vertical line. conductor 301, conductor 282,- vertical line 'wiper 153, side switch' wiper 160 to. the winding 316 of the back-bridge coil 166, springs 317 and 275 of the differential relay 165 to the battery lead 219, thence through I batteryB to ground G. The'energizing current for` the talking circuit,` in passing ithrough'theco'il 166, energizes saidcoil and causes the armature to close the springs 273 and 318 in'contact. [At theinstant that .these two springs 273 and 318 engage, thecalling 'substation isthereby: vprovided with 'current for energizing its primary talking-1'appara tus. The ri-remit in this sa@ extends from ground Gr1 to the 'side' switch wiper 163, 130

105 the primary winding' 313 of the -induction i dict'or' 3 1, grmarywinding^20 of the inducv .a :In A

These two windings' are so arranged that windln'g 272 ofthe V differential relay 165, ro-

2 taryv linel re1gy12 5 3, 't`uuk conductors 26.9, 256,271, 245- and 241 tothe rotary' line contion coil '1 -trensmitter183 springs 37 -38ft0 the vertical line conductor 30, trunk conductors 244', 264, 255 and 268, 'vertilcal line 'relay 152' throng .the windingv 270 10 of thel diere'ntiaA rela 165 thence to the battery lead 219, and't ound'- G. It will be' seen that' the two wind ings 270 and 272 of the differential relay 165 Y are includedinthe circuit that provides they calling subscriber with talking current.

when the current passes through th'exnin. `this manner the differential relay' 165 does not energize. Since the talking current flow- 2J ing to the calling subscriber passes through the'vertical and rotary line relays' 152 and 153, these two relays, as' soon as the said circuit i's' established?, become energized and attract their respective armatures, thereby placing the trunk-release springs 319 and 320 m contact.;4 l*This would result in the release of the'connecto'r'were it not furthe fact that 'the conneotionbetweenthe release magnet 164 and the .non-grounded battery' ternlnal sprn 275 and 276. The primary windings an A313 of the stations A and A', respecltively 'are' now 'connected in series in a circuit through the condensers 321 `and 322atlthe connex'z'tor.v The receivers 2 and 3080i the two 'substations in lquestif'm are each in series in e'loca'l circuit with their res ective' secondary windings 21 and 322 o the induetion coils 19 and 314, and the two subscribers may communicate lwith each otherin the usual manner since' their primary/'circuits are chargedywith a suitable cilrrentfroml the centr'nlorjcoinmon battery B, as already explin'ed. lf" v i After the two subscribers have completed their conversation, the nfront' release occurs when the'culling subscriber restores his i'e' ceiver 2-t0' the switch-hook 3, therebypress- :50i ing the-'release .springs 7 8 and `9 'into engagemenn whchengagement places the lifne f conductors and 31 in connection with the substation ground G. The 'groundingof the rotary line conductor 31 4produces a ces.-

' sation of the flow of current. through the rotary line relay 153*l and the winding mff :he differential 'muy 165. This is brouv h'tl-about by short-circuiting these two` win mg's inv series 'through ground. The

short-clrcuit extends from ground G to the rotar line conductor .31, tru-nk conductors 241, 4&5, 271;- 256 and 2,69 to the-rotary' line relay 153, winding 272 of thev differential .relay to the springs 273 and 318, to the M! side switch wiper 163 and to ground G1". The

rough battery B to.

The engagement 'of' the' spr-ings 'and through the winding.- 2720 the. f diiferent tact'. Simultaneously@withithegreenergigfig f' is interrupted beweert .the differential muy.4

cuit through the 'release magnetfof' shown in heavy. lines'in Figs. 1 and 2,v

vtot

153,' e154* and/J 155' 'and finie sinY l 122., releaseL relay armature-andremains rotary line -relay becoI- IQS denergized,

the trunk'frelease spring-319 'recedes current, the said relay,` becomes operativelyy energized; The. current-How'jjthrouglr the" said -felny 'extendssf-oirl g'l-Olllld (if GQ the release sp1-ings 7,8.anfd 9,-to' the Vertical l'iiie' f f conductor 30,; trunk conductore 240;', 244, 261, 255-.and268, i'f'ei'tifguly line'jA 1'elay'rli52, 75@A winding 2W-ofthe;l differential, relayflfi' the battery lead 219, t.hence thr0ugh battery B, to ground1 (3;, The energizatiox 1 off-'the Vdiii'erent-iul'r'xlay 165,' as abord, produces a' eey 11266; .wi

when the springs'BN :2T-5' which -relay` 166,', 'n 'pon ,ref ltoil-ing; 2173 and 31,810' .ensei-gage,- and urespring j 273 to come inl'contafjt with thespring'27lf l' I uref nor-mall position. Therel j'ase clay 51 b" I ingiucludedin the-faboverelea also'energizesand operates'tp", springs 324 and?A 325 in oont 'ct,f. wh`eieby all', series' energizing: ci'rcuit' is '-jestublishedfjll through the back-release relay, .13.3 fof. the selector D and the' 'releaser magnet- .136 O the selector' This-.circuit jextends .lfrom ground Gt through -the side '-svyitel-1 wipery y 133,- conductor. 259, 'prif" 120, vate wiper 250, 'conductor" 257, release'relay. springe-324 and 325, through weirdest-eef- 'magnet 136 to the .j bgttBIy--- l'ead 219, thiej arrhes@ release rela-y 1355,I upon e rg1zmg,.operates to close 'the springs 326 aud-325 in contact, 150 

